Patent Document 1 discloses a conventional method for forming an insulating separation structure at lower cost without using an SOI (Silicon on Insulator) substrate for a semiconductor device including a composite integrated circuit (hereinafter referred to as a composite IC). In particular, the following describes the method stated in Patent Document 1 for manufacturing a semiconductor device.
Initially, a trench for surrounding elements and each of the elements on one surface of a silicon substrate is formed. Next, a trench separation structure is configured by forming an insulation film through, for example, thermal oxidation to cover an inner wall surface of the trench, and forming a Poly-Si layer on the insulation film to embed the trench. Subsequently, a support substrate is bonded on a front surface of the silicon substrate, and then the insulation film is exposed by grinding a rear surface of the silicon substrate to a bottom surface of the trench. A region formed by various elements is surrounded by a trench separation structure and the insulation layer on the rear surface of the silicon substrate by bonding a support body on the rear surface of the silicon substrate through the insulation layer. Thus, it is possible to attain an insulating separation structure between elements without using an SOI substrate, and produce the insulating separation structure at lower cost.
However, insulation breakdown and lower yield of product manufacture are caused by insufficient film thickness of the insulation film formed on the inner wall of the trench. In addition, manufacturing cost is increased as an oxidation process for forming an insulation film or a process for embedding a Poly-Si layer is necessary, and a process for forming a trench separation structure is necessary.
[Patent Document 1] JP-2001-127149 A